The response of Hyssopus pallidus to hosts previously parasitised by Ascogaster quadridentata: heterospecific discrimination and host quality

1. Two basic tenets of competition among parasitoids, that taxonomically distinct parasitoids are unable to discriminate against hosts that have previously been attacked by a competitor and that previous parasitism reduces the quality of a host, were tested by monitoring the oviposition response of Hyssopus pallidus, a gregarious ectoparasitoid, to healthy codling moth larvae and codling moth larvae that had previously been parasitised by a solitary endoparasitoid, Ascogaster quadridentata. 2. Hyssopus pallidus accepted both categories of host larva for oviposition when its competitor was constrained as a first‐instar larva by the diapause development of its host, but discriminated against previously parasitised host larvae when its competitor was present as a larger larva in a non‐diapausing host. 3. Hyssopus pallidus distinguished between the two categories of host larva by allocating twice as many eggs to host larvae previously parasitised by A. quadridentata, a response that was not influenced by previous oviposition experience. 4. The larger clutch sizes allocated to previously parasitised host larvae produced twice as many female progeny, each of a typical size, such that the total biomass was twice that produced from the smaller clutches laid on healthy host larvae. Possible confounding influences of host age and diapause are discounted. 5. These results demonstrate that interspecific discrimination does occur in H. pallidus and that host quality can be improved through previous parasitism by an endoparasitoid. Although interspecific discrimination appears rare among insect parasitoids, it may have been overlooked among ectoparasitoids and requires examination of the fitness consequences of interspecific interactions to clarify its adaptive significance.     

Rapid morphological change in stream beetle museum specimens correlates with climate change

Abstract 1. Climate change has been occurring at unprecedented rates and its impacts on biological populations is beginning to be well documented in the literature. For many species, however, long‐term records are not available, and trends have not been documented. 2. Using museum specimens from southern USA, we show that the stream‐dwelling beetle Gyretes sinuatus has shown an 8% increase in body size and change in body shape (fineness ratio) from 1928 to 1988. Any directional morphological change observed over time could be an indicator of a microevolutionary response. 3. During these 60 years, there have also been changes in temperature, precipitation, and location of collection sites. Unlike the global trend, mean annual temperature in the region has decreased, and furthermore, total annual precipitation has increased. By investigating how these various ecological and geographical variables may affect body size and shape, we can examine which pressures may promote larger and/or thinner beetles. 4. Results indicate that mean annual temperature was the most predictive variable for the change in size and shape. We suggest there is an adaptive role for temperature on body size and shape of stream dwelling organisms. 5. We found that museum specimens can be invaluable resources of information when collection date and location information is available. We promote the use of such specimens for future studies of the morphological response to climate change.     

The effects of temperature, pH and water hardness on winter starvation of young-of-the-year smallmouth bass, Micropterus dolomieui Lacepede

Year-class strength in northern populations of smallmouth bass is strongly influenced by winter starvation of young-of-the-year. We examined starvation among young bass under both winter and summer light and temperature conditions. During starvation, body condition declines to a specific level and then the fish dies. Body condition at death is a well defined function of body size that remains relatively constant over a wide range of environmental conditions. Starvation rate varies systematically with body size, temperature, pH and water hardness. Available stored energy increases more rapidly with body size than starvation rate. Therefore, lifetime under starvation conditions tends to increase with increasing body size. The Q₁₀ for starvation rate over the temperature range 2.5-8° C is 2.2. Starvation rate increases as pH declines from 7.0-4.9: the rate at pH 4.9 is ∼ 1.25 times the rate at pH 7 Starvation rate decreases as Ca concentration increases from 1 mgl⁻¹ to 80mgl⁻¹: the rate at 80 mg Ca 1⁻¹ is ∼0.80 times the rate at 1 mgl⁻¹.     

SEXUAL SIZE DIMORPHISM AND REPRODUCTIVE INVESTMENT BY FEMALE SPIDERS: A COMPARATIVE ANALYSIS

We investigate the association between female reproductive investment, absolute size, and sexual size dimorphism in spiders to test the predictions of the fecundity-advantage hypothesis. The relationships between absolute size and sexual size dimorphism and aspects of female reproductive output are examined in comparative analyses using phylogenetically independent contrasts. We provide support for the idea that allometry for sexual dimorphism is the result of variation in female size more so than male size. Regression analyses suggest selection for increased fecundity in females. We argue that fecundity selection provides the only general explanation for the evolution of sexual size dimorphism in spiders.     

Preparation of a monolithic capillary column with immobilized alpha-mannose for affinity chromatography of lectins

A simple method for the preparation of an affinity monolithic (also called continuous bed) capillary column for alpha-mannose-specific lectins is described. 2-Hydroxyethyl methacrylate in combination with (+)-N,N -diallyltartardiamide (DATD) and piperazine diacrylamide (PDA, 1,4-bisacryloyl-piperazine) as crosslinkers, were used as monomers for the monolith. After oxidation of DATD with periodate, alpha-mannose with spacer was bound to the aldehyde groups of the polymeric skeleton via reductive amination to form an affinity column for the separation, enrichment or binding studies of mannose-specific lectins. The permeability of the column was excellent. The porosity of the monolith was investigated by scanning electron microscope (SEM) and inverse size exclusion chromatography (ISEC). The affinity of the monolith was evaluated by frontal analysis (FA) and fluorescence microscopy (FM) using fluorescently labeled concanavalin (Con A). Frontal affinity chromatography showed a specific interaction of two different lectins with the alpha-mannose-modified monolith. According to FM the affinity sites were evenly distributed over the monolithic bed.     

The use of Quantitative Agarose Gel Electrophoresis for rapid analysis of the integrity of protein-DNA complexes

Recent biochemical studies evaluated the affinity of histones to DNA in the context of nucleosome core particle (NCP). These have indicated a concentration-dependence for nucleosome stability. However, when studying chromatin the preferred templates are nucleosome arrays (NA) and not the NCP. Biochemical methods are poorly suited for structural analysis of chromatin. To overcome that technical hindrance, and investigate the effect of concentration on stability of the histone-DNA interactions, we have applied the multigel Quantitative Agarose Gel Electrophoresis (QAGE) method to in vitro-assembled nucleosomal arrays. The results demonstrated the method to be extremely valuable for the evaluation of the effect of low concentration on NA. However, QAGE is a fairly time-demanding and complex method. To maximize the efficiency of use of this technology, we devised a protocol that allowed for multiple sets of templates to be analyzed simultaneously. Briefly, samples can be loaded at regular intervals and analyzed individually for their molecular composition. The technique presented in this study describes the calibration steps and proof of concept necessary to validate the use of multiple loading of multigel to evaluate the composition of nucleosomal arrays as a function of concentration.     

Geographical and within-population variation in the globeflower–globeflower fly interaction: the costs and benefits of rearing pollinator’s larvae

Interspecific interactions can vary within and among populations and geographical locations, and this variation can influence the nature of the interaction (e.g. mutualistic versus antagonistic) and its evolutionary stability. Globeflowers are exclusively pollinated by flies whose larvae feed only on their seeds. Here we document geographical variability in costs and benefits in globeflowers in sustaining their pollinating flies throughout the range of this arctic-alpine European plant over several years. A total of 1,710 flower heads from 38 populations were analysed for their carpel, egg and seed contents. Individual and population analyses control for the confounding influences of variation in both: (1) population traits, such as fly density and egg distribution among flower heads; and (2) individuals traits, such as carpel and egg numbers per flower head. Despite considerable variation in ecological conditions and pollinator densities across populations, large proportions (range 33–58%) of seeds are released after predation, with a benefit-to-cost ratio of 3, indicating that the mutualism is stable over the whole globeflower geographical range. The stability of the mutualistic interaction relies on density-dependent competition among larvae co-developing in a flower head. This competition is revealed by a sharp decrease in the number of seeds eaten per larva with increasing larval number, and is intensified by non-uniform egg distribution among globeflowers within a population. Carpel number is highly variable across globeflowers (range 10–69), and flies lay more eggs in large flowers. Most plants within a population contribute to the rearing of pollinators, but some pay more than others. Large globeflowers lose more seed to pollinator larvae, but also release more seed than smaller plants. The apparent alignment of interests between fly and plant (positive relationship between numbers of seeds released and destroyed) is shown to hide a conflict of interest found when flower size is controlled for.